ABSTRACT Dozens of drugs have failed in clinical trials for the inflammatory lung disease ARDS (acute respiratory distress syndrome), largely due to 3 pharmacological challenges particular to ARDS: ARDS patients have multi-system organ failure, so cannot tolerate off-target drug side effects; the column of liquid covering alveoli prevents effective inhaled delivery; dozens of signaling pathways underlie ARDS, so modulating just one will not work. To overcome these 3 challenges, we designed M-LACs, which are 100-nanometer lipid spheres (liposomes), loaded with multiple drugs, and coated with targeting tags that cause them to massively accumulate in the capillaries of the alveoli (air sacs of the lungs). We have previously published on the benefits of M-LACs targeted to alveolar endothelial cells, but have long seen the need to target the other major alveolar capillary cell type, alveolar marginated neutrophils. Here we introduce new targeting tags that can massively concentrate M-LACs in alveolar neutrophils. With the new ability to target LACs to both endothelium and neutrophils, we can now answer fundamental questions in ARDS biology (Aim 1) and general pharmacology (Aim 2), while radically improving M-LACs as a therapy for ARDS (Aim 3). Aim 1: In ?ex vivo? human lungs and ?in vivo mouse models of ARDS, we quantify the relative number of marginated neutrophils compared to naive cases, and we will measure how well neutrophils and endothelial take up M-LACs. Aim 2: We will test the ?depot theory? of targeted drug delivery, which says drugs efficiently elute from targeted cells to their neighbors. We will test whether drugs meant to act in neutrophils (e.g., neutrophil elastase inhibitors) will ameliorate ARDS-like phenotypes the same or worse if targeted to endothelial cells, and vice versa. Aim 3: We will identify the principles of combination therapy. We hypothesize that the most efficacious combinations will be a pair of neutrophil- and endothelial-modulating drugs (e.g., as opposed to 2 endothelial-modulating drugs). By the end of these studies, we will have uncovered new ARDS biology and answered fundamental questions in pharmacology. Additionally, we will have created a highly optimized therapy for ARDS that we will have tested in multiple mouse models of ARDS and in human lungs.